The present invention relates to a superconducting integrated circuit using Josephson junctions and, more particularly, to a polarity-convertible Josephson driver circuit capable of injecting a current into a driven line such as a word or bit line of the memory cell array of the superconducting memory integrated circuit and arbitrarily reversing the direction of the current.
FIG. 9 shows an equivalent circuit for explaining a conventionally known polarity-convertible Josephson driver circuit (the Spring National Convention of the Institute of Electronics and Communication Engineers of Japan, 1988, C-66, "Polarity-Convertible Driver Circuits"). This prior art will be described below with reference to FIG. 9.
As shown in FIG. 9, a conventional polarity-convertible Josephson driver circuit comprises four magnetic coupling Josephson gate circuits G.sub.1 G.sub.2, G.sub.3, and G.sub.4, three resistors R.sub.1, R.sub.2, and R.sub.L, and a driven line L. In a memory circuit, the driven line L corresponds to the word or bit line of a memory cell array.
In this driver circuit, when a signal is input to a control signal input terminal S.sub.1 while a bias current is supplied to bias input terminals B.sub.1 and B.sub.2, the magnetic coupling Josephson gate circuits G.sub.1 and G.sub.3 are switched from a superconducting state to a voltage state, and the bias current is injected from an output terminal O.sub.1 into the driven line L through the resistor R.sub.1. The bias current flowing in the driven line L flows into ground through the magnetic coupling Josephson gate circuit G.sub.4. With the above operation, an output current can be generated by the driven line L in the clockwise direction in FIG. 9.
On the other hand, when a signal is input to a control signal input terminal S.sub.2, the magnetic coupling Josephson gate circuits G.sub.2 and G.sub.4 are switched from a superconducting state to a voltage state, and a bias current is injected from an output terminal O.sub.2 into the driven line L through the resistor R.sub.2. The bias current flowing in the driven line L flows into ground through the magnetic coupling Josephson gate circuit G.sub.3. With the above operation, an output current can be generated by the driven line L in the counterclockwise direction in FIG. 9.
As described above, the driver circuit can realize a polarity-convertible operation capable of injecting a current into the driven line L and arbitrarily reversing the direction of the current.
In this prior art, however, since the four magnetic coupling Josephson gate circuits (two-junction SQUID gates) are used, the circuit area is increased, and large-scale integration cannot be easily performed. In addition, since control lines respectively connected to the control signal input terminals S.sub.1 and S.sub.2 must be magnetically coupled to the set of two magnetic coupling Josephson gate circuits G.sub.1 and G.sub.3 and the set of two magnetic coupling Josephson gate circuits G.sub.2 and G.sub.4, respectively, the inductances of the control lines are increased, and the driver circuit cannot be easily operated at high speed.
Since the magnetic coupling Josephson gate circuits are used, an input signal current relatively larger than an output current is required. Furthermore, since the inductances of the control lines are increased, the driver circuit cannot be easily operated at high speed.